1. Field of the Invention
The present invention relates generally to a tracking signal generating device for obtaining a tracking error signal for positioning an optical head or a magnetic head in recording and/or reproducing information with respect to an information recording medium such as a high-density floppy disk, optical disk, or the like and to a magnetic recording/reproducing system carrying out tracking control using the tracking signal generating device.
2. Related Background Art
The intervals between tracks where a series of information is recorded are reduced with the increase in recording density with which information is recorded on a magnetic disk such as a floppy disk. This makes it difficult to position a magnetic head or the like in a direction perpendicular to the tracks with a mechanical precision. Consequently, an optical positioning technique has been required.
For instance, in a high-density floppy disk, tracks formed of tracking pit rows are arranged at an interval of about 20 xcexcm so that a magnetic head can track information tracks arranged at an interval of about 10 xcexcm. In this case, using an optical system with an numerical aperture NA of about 0.04 on a disk side with a wavelength of a light source of 780 nm, a tracking error signal can be obtained. The tracks to be tracked are formed of pit rows whose lengths are 40 to 70 xcexcm. The lengths of the pit rows are determined depending on the radial position so that signals from the tracks obtained at a revolution rate of 720 per minute have a frequency of 20 kHz. A conventional example used for obtaining a tracking signal from such a disk is described with reference to FIG. 15 as follows.
Light emitted from a semiconductor laser 101 as a light source is incident on a diffraction grating 162 provided at a first plane of a diffraction element 160 to generate xc2x11st-order diffracted lights (not shown in the figure). In this case, zero-order light is referred to as a main beam (M) and xc2x11st-order diffracted lights as sub-beams (S1 and S2).
The main beam and the sub-beams pass through a diffraction grating 161 provided at a second plane of the diffraction element 160 and are converged by a lens 104 as a converging means. The main beam and the sub-beams that have become converged lights are focused on a disk 107 as an information recording medium with an aperture being limited so that a desirable numerical aperture (NA) is obtained through an aperture 105.
With reference to FIG. 16, the relationship between the beams and a pit row on the disk is described. There are tracks 204 formed of rows of pits 205 on the disk 107. On the disk 107, a beam row formed of a main beam (M) 201 and two sub-beams (S1 and S2) 202 and 203 is positioned so as to have a predetermined angle xcex80 with respect to a track 204 of the disk 107.
In the figure, l denotes an interval between M and S1 or S2 on the disk 107, Tp indicates an interval between two adjacent tracks 204, and Tpp denotes a radial distance from M to S1 or S2. A tangential direction is a circumferential direction in the disk 107 and a radial direction is a direction of the radius of disk 107.
Returning to FIG. 15, the main beam and the sub-beams reflected from the disk 107 pass through the aperture 105 and the lens 104 again and are diffracted by the diffraction grating 161, and then enter a photodetector 108R or 108L.
The photodetectors 108R and 108L include a plurality of detection regions to receive the main beam and the sub-beams separately, and output signals corresponding to the quantity of received beams. The three beams irradiate locations different in a direction perpendicular to the tracks on the disk 107. Therefore, signals obtained from the three detection regions are different in modulation degree from one another. Through calculation of these signals by a tracking error signal generating device shown in FIG. 17, the relative positional relationship between the track and the beam irradiation locations can be detected.
Next, the following description is directed to the tracking error signal generating device shown in FIG. 17. One sub-beam S1 of the two sub-beams is received by a detection region 301 of the photodetector 108L and a detection region 304 of the photodetector 108R and the respective photodetectors 108L and 108R output currents corresponding to the quantity of the received beams. The currents are converted to a voltage signal by an I-V amplifier 401, which then is output. Similarly, the main beam M is received by a detection region 302 of the photodetector 108L and a detection region 305 of the photodetector 108R, and current signals corresponding to the quantity of the received beams are converted to a voltage signal by an I-V amplifier 402, which then is output. Furthermore, another sub-beam S2 also is received by a detection region 303 of the photodetector 108L and a detection region 306 of the photodetector 108R, and current signals corresponding to the quantity of the received beams are converted to a voltage signal by an I-V amplifier 403, which then is output.
In this case, generally, the three beams M, S1, and S2 generated by the diffraction grating 161 are affected by diffraction efficiency and their quantities received by the photodetectors 108L and 108R are different from one another. Therefore, the I-V amplifiers 401, 402, and 403 have a gain ratio canceling the influence of the diffraction efficiency.
Next, the signals output from the I-V amplifiers 401, 402, and 403 are input into bandpass filters 404, 405, and 406, respectively, and are subjected to bandpass with signals of 20 kHz as a frequency used for the reproduction of a pit row being centered. The signals output from the bandpass filters 404, 405, and 406 are input into detection circuits 407, 408, and 409, respectively. From the signals of 20 kHz, their envelope signals are extracted. The amplitudes of the envelope signals reflect the positional relationships between the track and the beams on the disk 107 and vary accordingly.
The signal output from the detection circuit 407 is indicated as Ss1, the signal output from the detection circuit 408 as Sm, and the signal output from the detection circuit 409 as Ss2.
Further, an amplitude level of the signal Sm (xc2xd of the difference between a maximum value and a minimum value of the signal Sm when an optical beam moves for a distance equal to or more than the interval Tp in the radial direction on the disk 107) is indicated as Lm, amplitude levels of the signals Ss1 and Ss2 as L1 and L2, respectively, a phase of the signal Ss1 with respect to the signal Sm as xcfx861, and a phase of the signal Ss2 with respect to the signal Sm as xcfx862. In this case, the signals Sm, Ss1, Ss2 and the phases xcfx861 and xcfx862 are expressed by
Sm=Lmxc3x97sin xcex8,xe2x80x83xe2x80x83Eq. 1
Ss1=L1xc3x97sin(xcex8xe2x88x92xcfx861),xe2x80x83xe2x80x83Eq. 2
Ss2=L2xc3x97sin(xcex8+xcfx862), andxe2x80x83xe2x80x83Eq. 3
xcfx861=xcfx862=2xcfx80xc3x97Tpp/Tp,xe2x80x83xe2x80x83Eq. 4
wherein xcex8 can be obtained by xcex8=2xcfx80xc3x97Lj/Tp, where Lj denotes a radial distance between the track 204 and the main beam M.
Next, a differential operational circuit 410 receives the signals Ss1 and Sm and outputs a difference signal Sa thereof. In addition, a differential operational circuit 411 receives the signals Sm and Ss2 and outputs a difference signal Sb thereof. These difference signals Sa and Sb are expressed by
Sa=Smxe2x88x92Ss1=Laxc3x97sin(xcex8+xcfx86a) andxe2x80x83xe2x80x83Eq. 5
Sb=Ss2xe2x88x92Sm=Lbxc3x97sin(xcex8+xcfx86b),xe2x80x83xe2x80x83Eq. 6
wherein the amplitude levels La and Lb of the signals Sa and Sb and the phase differences xcfx86a and xcfx86b are expressed by                               tan          ⁢                      xe2x80x83                    ⁢          φ          ⁢                      xe2x80x83                    ⁢          a                =                                            -              L1                        *            sin            ⁢                          xe2x80x83                        ⁢            φ            ⁢                          xe2x80x83                        ⁢            1                                              -              Lm                        +                          L1              *              cos              ⁢                              xe2x80x83                            ⁢                              φ                ⁢                1                                                                        Eq. 7                                La        =                                            Lm              2                        +                          L1              2                        +                          2              *              Lm              *              L1              *              cos              ⁢                              xe2x80x83                            ⁢              φ              ⁢                              xe2x80x83                            ⁢              1                                                          Eq. 8                                          tan          ⁢                      xe2x80x83                    ⁢          φ          ⁢                      xe2x80x83                    ⁢          b                =                                            -              L2                        *            sin            ⁢                          xe2x80x83                        ⁢                          φ              ⁢              2                                            Lm            -                          L2              *              cos              ⁢                              xe2x80x83                            ⁢                              φ                ⁢                2                                                                        Eq. 9                                Lb        =                                            Lm              2                        +                          L2              2                        +                          2              *              Lm              *              L2              *              cos              ⁢                              xe2x80x83                            ⁢              φ              ⁢                              xe2x80x83                            ⁢              2                                                          Eq. 10            
Then, a signal synthesizing circuit 412 receives the difference signals Sa and Sb and synthesizes a tracking error signal TE. This signal TE is expressed by
TE=xcex1jxc3x97Sa+xcex2jxc3x97Sb,xe2x80x83xe2x80x83Eq. 11
wherein xcex1j and xcex2j are given by
xcex1j=cos xcfx86j andxe2x80x83xe2x80x83Eq. 12
xcex2j=sin xcfx86j,xe2x80x83xe2x80x83Eq. 13
where xcfx86j is defined as
xcfx86j=xe2x88x92xcfx80/4+2xcfx80xc3x97c/Tp.xe2x80x83xe2x80x83Eq. 14
When a distance between a magnetic head 170 and the main beam M on the disk 107 is indicated as Lo-m, Lo-m is expressed by
Lo-m=nxc3x97Tp+c,xe2x80x83xe2x80x83Eq. 15
wherein n denotes an integer, 0 less than c less than Tp holds, and the values of xcex1j and xcex2j are determined by a control circuit 413 so that the tracking error signal TE crosses zero when the magnetic head is positioned on a track.
Practically, the device seeks to position the magnetic head 170 (FIG. 15) in the vicinity of a magnetic track on which predetermined magnetic data have been recorded, and the value of xcfx86j (i.e. the values of xcex1j and xcex2j) is determined through learning so that a maximum amplitude of signals can be obtained or a minimum error ratio can be achieved.
The following description is directed to the reason why the value of xcfx86j must be determined through learning. In a magnetic recording/reproducing system for recording or reproducing information using the magnetic head 170 and detecting the tracking error signal TE using the optical system, the distance Lo-m between the magnetic head and the main beam on the disk 107 must be at least several hundreds of micrometers to several millimeters. In other words, a point P1 where the magnetic head 170 contacts with the disk 107 and a focal point P2 of the main beam M scan different tracks on the disk 107.
In the assembly of the magnetic recording/reproducing system, when the point P1 is positioned exactly on a track of the disk 107, the distance Lo-m is adjusted so that the operating point of the tracking control is positioned in the midpoint of the amplitude of the tracking error signal TE. However, the disk 107 expands and contracts when the temperature or humidity varies and the track pitch Tp varies accordingly. In addition, disks used as the disk 107 may have variations in track pitch Tp, respectively. Therefore, the point P1 deviates from the track to be tracked and the information reproduction characteristic of the magnetic head 170 deteriorates considerably unless the value of xcfx86j (i.e. the values of xcex1j and xcex2j) is determined to correct the tracking error signal TE. In order to avoid such deterioration, the value of xcfx86j is determined through learning.
Values in a table recorded in a memory or the like are used as the values of xcex1j and xcex2j. Based on the tracking error signal TE thus obtained, the tracking control is carried out and the magnetic head 170 tracks an information track to write or readout information.
In a conventional operational circuit or method for obtaining the tracking error signal TE, when the positional relationship between a beam row formed of the main beam M and the two sub-beams S1 and S2 and a track formed of a pit row on the disk deviates from an ideal state, the amplitude level of the tracking error signal TE varies depending on the phase of the tracking error signal to be synthesized. In order to carry out stable tracking control, it is required that the amplitude level of the tracking error signal TE does not vary even when the tracking error signal TE is obtained in an arbitrary phase.
Therefore, the present invention is intended to solve the aforementioned problem, and it is an object of the present invention to provide a tracking signal generating device and method and a magnetic recording/reproducing system, which enable stable tracking control even in an arbitrary phase.
In order to achieve the above-mentioned object, a first tracking signal generating device according to the present invention includes a light source for emitting light, an optical system, photodetectors, position signal generating sections, intermediate signal generating sections, and a signal synthesizing circuit. With the optical system, an information recording medium with a track from which information can be readout optically is irradiated with the light emitted from the light source as at least three optical beams. The photodetectors receive optical beams reflected from the information recording medium. The position signal generating sections output three position signals Sm, Ss1, and Ss2 corresponding to a positional relationship between the three optical beams and the track from signals obtained corresponding to the quantity of the optical beams entering the photodetectors. The intermediate signal generating sections receive the three position signals Sm, Ss1, and Ss2, calculate differences between Sm and Ss1 and between Sm and Ss2 with the position signal Sm being taken as a reference, execute calculation for correction, and generate two intermediate signals Sa and Sb. The signal synthesizing circuit synthesizes a zero-crossing tracking signal in an arbitrary phase with respect to the track from the intermediate signals Sa and Sb. The intermediate signal generating sections execute the correction so that the intermediate signals Sa and Sb have same amplitude levels and are different in phase by xcfx80/2 rad in a track crossing direction, and output them.
In the tracking signal generating device, preferably the signal synthesizing circuit multiplies the two intermediate signals Sa and Sb input thereinto by coefficients xcex1 and xcex2 given by
xcex1=Cxc2x7sin xcfx86 and
xcex2=Cxc2x7cos xcfx86
or
xcex1=Cxc2x7cos xcfx86 and
xe2x80x83xcex2=Cxc2x7sin xcfx86,
where C and xcfx86 are constants, and adds them.
In order to achieve the above-mentioned object, a second tracking signal generating device according to the present invention includes a light source for emitting light, an optical system, photodetectors, position signal generating sections, a first variable gain amplifier, a second variable gain amplifier, a third variable gain amplifier, a fourth variable gain amplifier, a first differential operational circuit, a second differential operational circuit, and a signal synthesizing circuit. With the optical system, an information recording medium with a track from which information can be readout optically is irradiated with the light emitted from the light source as at least three optical beams. The photodetectors receive optical beams reflected from the information recording medium. The position signal generating sections output three position signals Sm, Ss1, and Ss2 corresponding to a positional relationship between the three optical beams and the track from signals obtained corresponding to the quantity of the optical beams entering the photodetectors. The first variable gain amplifier has a coefficient Fm1, receives the position signal Sm, and outputs a signal Fm1xc2x7Sm. The second variable gain amplifier has a coefficient Fm2, receives the position signal Sm, and outputs a signal Fm2xc2x7Sm. The third variable gain amplifier has a coefficient F1, receives the position signal Ss1, and outputs a signal F1xc2x7Ss1. The fourth variable gain amplifier has a coefficient F2, receives the position signal Ss2, and outputs a signal F2xc2x7Ss2. The first differential operational circuit receives the signals Fm1xc2x7Sm and F1xc2x7Ss1 output from the first and third variable gain amplifiers and obtains a difference signal Sa3 of the signals Fm1xc2x7Sm and F1xc2x7Ss1. The second differential operational circuit receives the signals Fm2xc2x7Sm and F2xc2x7Ss2 output from the second and fourth variable gain amplifiers and obtains a difference signal Sb3 of the signals Fm2xc2x7Sm and F2xc2x7Ss2. The signal synthesizing circuit multiplies the difference signals Sa3 and Sb3 from the first and second differential operational circuits by predetermined coefficients and adds them, which is output as a tracking signal. The coefficients Fm1, Fm2, F1, and F2 are determined with respect to the first to fourth variable gain amplifiers so that the difference signals Sa3 and Sb3 have the same amplitude level and are different in phase by xcfx80/2 rad in a track crossing direction.
In the second tracking signal generating device, preferably the respective coefficients Fm1, Fm2, F1, and F2 of the first to fourth variable gain amplifiers satisfy
Fm1/F1=L1xc3x97(cos xcfx861+sin xcfx861)/Lm,
Fm2/F2=L2xc3x97(cos xcfx862+sin xcfx862)/Lm, and
F1/F2=L2xc3x97|sin xcfx862|/(L1xc3x97|sin xcfx861|),
wherein xcfx861 denotes a phase difference between the position signals Sm and Ss1, xcfx862 a phase difference between the position signals Sm and Ss2, Lm an amplitude of the position signal Sm, L1 an amplitude of the position signal Ss1, and L2 an amplitude of the position signal Ss2.
In the second tracking signal generating device, preferably the signal synthesizing circuit multiplies the two difference signals Sa3 and Sb3 input thereinto by coefficients xcex1 and xcex2 given by
xcex1=Cxc2x7sin xcfx86 and
xcex2=Cxc2x7cos xcfx86
or
xcex1=Cxc2x7cos xcfx86 and
xcex2=Cxc2x7sin xcfx86,
where C and xcfx86 are constants, and adds them.
In order to achieve the above-mentioned object, a third tracking signal generating device according to the present invention includes a light source for emitting light, an optical system, photodetectors, position signal generating sections, a first differential operational circuit, a second differential operational circuit, and a signal synthesizing circuit. With the optical system, an information recording medium with a track from which information can be readout optically is irradiated with the light emitted from the light source as at least three optical beams. The photodetectors receive optical beams reflected from the information recording medium. The position signal generating sections output three position signals Sm, Ss1, and Ss2 corresponding to a positional relationship between the three optical beams and the track from signals obtained corresponding to the quantity of the optical beams entering the photodetectors. The first differential operational circuit receives the position signals Sm and Ss1 and outputs a difference signal Sa thereof. The second differential operational circuit receives the position signals Sm and Ss2 and outputs a difference signal Sb thereof. The signal synthesizing circuit multiplies the difference signals Sa and Sb output from the first and second differential operational circuits, respectively, by predetermined coefficients xcex1 and xcex2 and adds them, which is output as a tracking signal. The coefficients xcex1 and xcex2 are given by
xe2x80x83xcex1=(Cxc2x7cos xcfx86)/La and
xcex2=(Cxc2x7sin xcfx86)/Lb
or
xcex1=(Cxc2x7sin xcfx86)/La and
xcex2=(Cxc2x7cos xcfx86)/Lb,
wherein La and Lb denote amplitudes of the difference signals Sa and Sb, respectively, and C and xcfx86 are constants.
In order to achieve the above-mentioned object, a fourth tracking signal generating device according to the present invention includes a light source for emitting light, an optical system, photodetectors, position signal generating sections, a first differential operational circuit, a second differential operational circuit, a signal synthesizing circuit, and a variable gain amplifier. With the optical system, an information recording medium with a track from which information can be readout optically is irradiated with the light emitted from the light source as at least three optical beams. The photodetectors receive optical beams reflected from the information recording medium. The position signal generating sections output three position signals Sm, Ss1, and Ss2 corresponding to a positional relationship between the three optical beams and the track from signals obtained corresponding to the quantity of the optical beams entering the photodetectors. The first differential operational circuit receives the position signals Sm and Ss1 and outputs a difference signal Sa thereof. The second differential operational circuit receives the position signals Sm and Ss2 and outputs a difference signal Sb thereof. The signal synthesizing circuit multiplies the difference signals Sa and Sb output from the first and second differential operational circuits, respectively, by predetermined coefficients and adds them. The variable gain amplifier receives a signal output from the signal synthesizing circuit and multiplies it by a suitable coefficient, which is output as a tracking signal. In the variable gain amplifier, the suitable coefficient is determined so that the signal input into the variable gain amplifier has a predetermined amplitude level during track crossing.
In order to achieve the above-mentioned object, a first tracking signal generating method according to the present invention is carried out by irradiating an information recording medium with a track from which information can be readout optically with light emitted from a light source as at least three optical beams and receiving optical beams reflected from the information recording medium by photodetectors. The first tracking signal generating method includes: generating three position signals Sm, Ss1, and Ss2 corresponding to a positional relationship between the three optical beams and the track from signals obtained corresponding to the quantity of the optical beams entering the photodetectors; receiving the three position signals Sm, Ss1, and Ss2, calculating differences between Sm and Ss1 and between Sm and Ss2 with the position signal Sm being taken as a reference, executing calculation for correction, and generating two intermediate signals Sa and Sb so that they are different in phase by xcfx80/2 rad in a track crossing direction and have same amplitude levels; and synthesizing a zero-crossing tracking signal in an arbitrary phase with respect to the track from the intermediate signals Sa and Sb.
In the first tracking signal generating method, preferably the synthesizing of the zero-crossing tracking signal is executed by multiplying the two intermediate signals Sa and Sb by coefficients xcex1 and xcex2 given by
xcex1=Cxc2x7sin xcfx86 and
xcex2=Cxc2x7cos xcfx86
or
xcex1=Cxc2x7cos xcfx86 and
xcex2=Cxc2x7sin xcfx86,
where C and xcfx86 are constants, and adding them.
In order to achieve the above-mentioned object, a second tracking signal generating method according to the present invention is carried out by irradiating an information recording medium with a track from which information can be readout optically with light emitted from a light source as at least three optical beams and receiving optical beams reflected from the information recording medium by photodetectors. The second tracking signal generating method includes: generating three position signals Sm, Ss1, and Ss2 corresponding to a positional relationship between the three optical beams and the track from signals obtained corresponding to the quantity of the optical beams entering the photodetectors; multiplying the position signal Sm by a coefficient Fm1 to generate a signal Fm1xc2x7Sm; multiplying the position signal Sm by a coefficient Fm2 to generate a signal Fm2xc2x7Sm; multiplying the position signal Ss1 by a coefficient F1 to generate a signal F1xc2x7Ss1; multiplying the position signal Ss2 by a coefficient F2 to generate a signal F2xc2x7Ss2; calculating a difference signal Sa3 of the signals Fm1xc2x7Sm and F1xc2x7Ss1; calculating a difference signal Sb3 of the signals Fm2xc2x7Sm and F2xc2x7Ss2; and multiplying the difference signals Sa3 and Sb3 by predetermined coefficients and adding them, thus synthesizing a tracking signal. The coefficients Fm1, Fm2, F1, and F2 are determined so that the difference signals Sa3 and Sb3 have constant amplitude levels and are different in phase by xcfx80/2 rad in a track crossing direction.
In the second tracking signal generating method, preferably the coefficients Fm1, Fm2, F1, and F2 satisfy
Fm1/F1=L1xc3x97(cos xcfx861+sin xcfx861)/Lm,
Fm2/F2=L2xc3x97(cos xcfx862+sin xcfx862)/Lm, and
F1/F2=L2xc3x97|sin xcfx862|/(L1xc3x97|sin xcfx861|),
wherein xcfx861 denotes a phase difference between the position signals Sm and Ss1, xcfx862 a phase difference between the position signals Sm and Ss2, and Lm, L1, and L2 amplitudes of the position signals Sm, Ss1, and Ss2, respectively.
In the second tracking signal generating method, preferably the synthesizing of the tracking signal is executed by multiplying the two difference signals Sa3 and Sb3 by coefficients xcex1 and xcex2 given by
xcex1=Cxc2x7sin xcfx86 and
xcex2=Cxc2x7cos xcfx86
or
xcex1=Cxc2x7cos xcfx86 and
xcex2=Cxc2x7sin xcfx86,
where C and xcfx86 are constants, and adding them.
In order to achieve the above-mentioned object, a first magnetic recording/reproducing system according to the present invention includes a magnetic head, a light source for emitting light, an optical system, photodetectors, position signal generating sections, intermediate signal generating sections, and a signal synthesizing circuit. The magnetic head records or reproduces information with respect to an information recording medium with a track from which information can be readout optically. With the optical system, the information recording medium is irradiated with the light emitted from the light source as at least three optical beams. The photodetectors receive optical beams reflected from the information recording medium. The position signal generating sections output three position signals Sm, Ss1, and Ss2 corresponding to a positional relationship between the three optical beams and the track from signals obtained corresponding to the quantity of the optical beams entering the photodetectors. The intermediate signal generating sections receive the three position signals Sm, Ss1, and Ss2, calculate differences between Sm and Ss1 and between Sm and Ss2 with the position signal Sm being taken as a reference, execute calculation for correction, and generate two intermediate signals Sa and Sb. The signal synthesizing circuit synthesizes a zero-crossing tracking signal in an arbitrary phase with respect to the track from the intermediate signals Sa and Sb. The intermediate signal generating sections execute the correction so that the intermediate signals Sa and Sb have same amplitude levels and are different in phase by xcfx80/2 rad in a track crossing direction, and output them. Tracking control is carried out according to the tracking signal output from the signal synthesizing circuit.
In the first magnetic recording/reproducing system, preferably the signal synthesizing circuit multiplies the two intermediate signals Sa and Sb input thereinto by coefficients xcex1 and xcex2 given by
xcex1=Cxc2x7sin xcfx86 and
xcex2=Cxc2x7cos xcfx86
or
xcex1=Cxc2x7cos xcfx86 and
xcex2=Cxc2x7sin xcfx86,
where C and xcfx86 are constants, and adds them.
In order to achieve the above-mentioned object, a second magnetic recording/reproducing system according to the present invention includes a magnetic head, a light source for emitting light, an optical system, photodetectors, position signal generating sections, a first variable gain amplifier, a second variable gain amplifier, a third variable gain amplifier, a fourth variable gain amplifier, a first differential operational circuit, a second differential operational circuit, and a signal synthesizing circuit. The magnetic head records or reproduces information with respect to an information recording medium with a track from which information can be readout optically. With the optical system, the information recording medium is irradiated with the light emitted from the light source as at least three optical beams. The photodetectors receive optical beams reflected from the information recording medium. The position signal generating sections output three position signals Sm, Ss1, and Ss2 corresponding to a positional relationship between the three optical beams and the track from signals obtained corresponding to the quantity of the optical beams entering the photodetectors. The first variable gain amplifier has a coefficient Fm1, receives the position signal Sm, and outputs a signal Fm1xc2x7Sm. The second variable gain amplifier has a coefficient Fm2, receives the position signal Sm, and outputs a signal Fm2xc2x7Sm. The third variable gain amplifier has a coefficient F1, receives the position signal Ss1, and outputs a signal F1xc2x7Ss1. The fourth variable gain amplifier has a coefficient F2, receives the position signal Ss2, and outputs a signal F2xc2x7Ss2. The first differential operational circuit receives the signals Fm1xc2x7Sm and F1xc2x7Ss1 output from the first and third variable gain amplifiers and obtains a difference signal Sa3 of the signals Fm1xc2x7Sm and F1xc2x7Ss1. The second differential operational circuit receives the signals Fm2xc2x7Sm and F2xc2x7Ss2 output from the second and fourth variable gain amplifiers and obtains a difference signal Sb3 of the signals Fm2xc2x7Sm and F2xc2x7Ss2. The signal synthesizing circuit multiplies the difference signals Sa3 and Sb3 from the first and second differential operational circuits by predetermined coefficients and adds them, which is output as a tracking signal. The coefficients Fm1, Fm2, F1, and F2 are determined with respect to the first to fourth variable gain amplifiers so that the difference signals Sa3 and Sb3 have the same amplitude level and are different in phase by xcfx80/2 rad in a track crossing direction. Tracking control is carried out according to the tracking signal output from the signal synthesizing circuit.
In the second magnetic recording/reproducing system, preferably the respective coefficients Fm1, Fm2, F1, and F2 of the first to fourth variable gain amplifiers satisfy
Fm1/F1=L1xc3x97(cos xcfx861+sin xcfx861)/Lm,
Fm2/F2=L2xc3x97(cos xcfx862+sin xcfx862)/Lm, and
F1/F2=L2xc3x97|sin xcfx862|/(L1xc3x97|sin xcfx861|),
wherein xcfx861 denotes a phase difference between the position signals Sm and Ss1, xcfx862 a phase difference between the position signals Sm and Ss2, and Lm, L1, and L2 amplitudes of the position signals Sm, Ss1, and Ss2, respectively.
In the second magnetic recording/reproducing system, preferably the signal synthesizing circuit multiplies the two difference signals Sa3 and Sb3 input thereinto by coefficients xcex1 and xcex2 given by
xcex1=Cxc2x7sin xcfx86 and
xcex2=Cxc2x7cos xcfx86
or
xcex1=Cxc2x7cos xcfx86 and
xcex2=Cxc2x7sin xcfx86,
where C and xcfx86 are constants, and adds them.
In order to achieve the above-mentioned object, a third magnetic recording/reproducing system according to the present invention includes a magnetic head, a light source for emitting light, an optical system, photodetectors, position signal generating sections, a first differential operational circuit, a second differential operational circuit, and a signal synthesizing circuit. The magnetic head records or reproduces information with respect to an information recording medium with a track from which information can be readout optically. With the optical system, the information recording medium is irradiated with the light emitted from the light source as at least three optical beams. The photodetectors receive optical beams reflected from the information recording medium. The position signal generating sections output three position signals Sm, Ss1, and Ss2 corresponding to a positional relationship between the three optical beams and the track from signals obtained corresponding to the quantity of the optical beams entering the photodetectors. The first differential operational circuit receives the position signals Sm and Ss1 and outputs a difference signal Sa thereof. The second differential operational circuit receives the position signals Sm and Ss2 and outputs a difference signal Sb thereof. The signal synthesizing circuit multiplies the difference signals Sa and Sb output from the first and second differential operational circuits, respectively, by predetermined coefficients xcex1 and xcex2 and adds them, which is output as a tracking signal. The coefficients xcex1 and xcex2 are given by
xcex1=(Cxc2x7cos xcfx86)/La and
xcex2=(Cxc2x7sin xcfx86)/Lb
or
xcex1=(Cxc2x7sin xcfx86)/La and
xcex2=(Cxc2x7cos xcfx86)/Lb,
wherein La and Lb denote amplitudes of the difference signals Sa and Sb, respectively, and C and xcfx86 are constants. Tracking control is carried out according to the tracking signal output from the signal synthesizing circuit.
In order to achieve the above-mentioned object, a fourth magnetic recording/reproducing system according to the present invention includes a magnetic head, a light source for emitting light, an optical system, photodetectors, position signal generating sections, a first differential operational circuit, a second differential operational circuit, a signal synthesizing circuit, and a variable gain amplifier. The magnetic head records or reproduces information with respect to an information recording medium with a track from which information can be readout optically. With the optical system, the information recording medium is irradiated with the light emitted from the light source as at least three optical beams. The photodetectors receive optical beams reflected from the information recording medium. The position signal generating sections output three position signals Sm, Ss1, and Ss2 corresponding to a positional relationship between the three optical beams and the track from signals obtained corresponding to the quantity of the optical beams entering the photodetectors. The first differential operational circuit receives the position signals Sm and Ss1 and outputs a difference signal Sa thereof. The second differential operational circuit receives the position signals Sm and Ss2 and outputs a difference signal Sb thereof. The signal synthesizing circuit multiplies the difference signals Sa and Sb output from the first and second differential operational circuits, respectively, by predetermined coefficients and adds them. The variable gain amplifier receives a signal output from the signal synthesizing circuit and multiplies it by a suitable coefficient, which is output as a tracking signal. In the variable gain amplifier, the suitable coefficient is determined so that the signal input into the variable gain amplifier has a predetermined amplitude level during track crossing. Tracking control is carried out according to the tracking signal output from the variable gain amplifier.
According to the above-mentioned configurations, even when the three optical beams are not aligned on a straight line, an ideal tracking error signal with a constant amplitude level can be obtained and the variation in gain of tracking servo can be suppressed to 0 dB, thus achieving stable tracking control. As a result, signals can be readout with a low error ratio.
Since the shift of the three beams from the straight line is acceptable, high precision alignment of the optical system is not required, thus reducing the cost of the optical system. In addition, since variations in the alignment are acceptable, the degree of freedom in design of the optical system is increased.
Further, even when the angle formed between the track and the beam row formed of three optical beams is different from an ideal angle, a tracking error signal with a constant amplitude is obtained. Therefore, it is not required to adjust the angle formed between the beam row and the track, thus reducing the manufacturing cost of the magnetic recording/reproducing system using this tracking signal generating device.
In addition to the case where the angle formed between the beam row and the track is different from an ideal angle xcex80, even in a case where the amplitude levels of the signals output from the photodetectors vary, a tracking error signal with a constant amplitude can be obtained. Therefore, adjustment of not only the angle formed between the beam row and the track but also the amplitude levels becomes unnecessary, thus reducing the manufacturing cost of the magnetic recording/reproducing system using this tracking signal generating device.